Workpiece processing systems commonly employ vacuum transfer robots to transfer workpieces (e.g., semiconductor wafers) from one or more sub-atmospheric storage receptacles (e.g., load locks) to a processing chamber, or between processing chambers. The vacuum transfer robot, which may reside within a transfer chamber positioned between the load locks and a processing chamber, includes an extendable arm having an end effector attached thereto. To move a selected workpiece from a load lock into a processing chamber, the transfer robot first extends its arm into the load lock and picks up the selected wafer such that the wafer rests on the end effector. The vacuum transfer robot then retracts its arm, rotates to point its arm toward the processing chamber, and extends its arm into the processing chamber. To complete the transfer process, the robot places the workpiece on a pedestal assembly (e.g., an electrostatic chuck) located within the processing chamber. After the transfer process has been completed, the robot's arm is retracted from the processing chamber, certain operating conditions are created in the processing chamber (e.g., high temperatures and near-vacuum pressure levels), and processing commences.
It is important for the overall success of the processing step that the workpiece transfer robot is capable of repeatedly and reliably placing a workpiece at a precise location on the processing chamber pedestal assembly. Thus, to ensure that the robot's movements are accurately coordinated with the physical layout of the particular processing system in which the robot is employed, the workpiece transfer robot undergoes a teaching process prior to workpiece processing. In conventional robot teaching processes, the transfer chamber and processing chamber are vented to atmosphere, the lids are opened, and a fixture is placed on the pedestal assembly. Utilizing the fixture as a reference point, an operator moves the robot's end effector to an ideal workpiece transfer position, either manually or via a “teach pad” remote control, and the end effector's coordinates are recorded. The robot's controller is then programmed to move the end effector to the coordinates corresponding to the ideal transfer position before placing a workpiece on the processing chamber pedestal assembly.
Although conventional transfer robot teaching processes of the type described above are generally sufficient for teaching a robot an ideal workpiece transfer position, such processes may be subject to inaccuracies in determining the ideal workpiece transfer position. For example, such conventional teaching processes rely on an operator to position the robot's end effector and pedestal fixture and may consequently be subject to human error. More importantly, such conventional teaching processes are performed with the chambers' lids open and, therefore, cannot be carried out under normal operating conditions. As a result, conventional transfer robot teaching processes are unable to compensate for thermal expansion and deflection resulting from the high temperatures and sub-atmospheric pressures experienced during actual workpiece processing. Moreover, in the event that a workpiece transfer robot becomes misaligned during workpiece processing, conventional teaching processes generally require that the processing chamber is cleaned, cooled, and vented before the transfer robot may be re-trained and workpiece processing resumed.
In view of the above, it would be desirable to provide a method and apparatus for teaching a workpiece transfer robot that overcomes the above-noted disadvantages. In particular, it would be desirable if such a teaching method were capable of being performed at or near normal certain operating conditions to reduce inaccuracies introduced by thermal expansion and vacuum deflection. It would also be desirable if such a teaching method eliminated the need for manually-placed fixtures and for cleaning, cooling, and venting the processing chamber to re-train the workpiece transfer robot. Finally, it would be desirable if the teaching method utilized one or more sensors (e.g., a light sensor, such as a pyrometer) pre-existing in a conventional processing chamber. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.